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91.
92.
D.S. Franzblau 《Discrete Applied Mathematics》2008,156(10):1623-1632
A set cover for a set S is a collection C of special subsets whose union is S. Given covers A and B for two sets, the set-cover difference problem is to construct a new cover for the elements covered by A but not B. Applications include testing equivalence of set covers and maintaining a set cover dynamically. In this paper, we solve the set-cover difference problem by defining a difference operation A-B, which turns out to be a pseudocomplement on a distributive lattice. We give an algorithm for constructing this difference, and show how to implement the algorithm for two examples with applications in computer science: face covers on a hypercube, and rectangle covers on a grid. We derive an upper bound on the time complexity of the algorithm, and give upper and lower bounds on complexity for face covers and rectangle covers. 相似文献
93.
Schlosser 《Constructive Approximation》2008,19(2):163-178
Abstract. We give an r -dimensional generalization of H. S. Shukla's very-well-poised
8
ψ
8
summation formula. We work in the setting of multiple basic hypergeometric series very-well-poised over the root system
A
r-1
or, equivalently, the unitary group U(r) . Our proof, which is already new in the one-dimensional case, utilizes an A
r-1
nonterminating very-well-poised
6
φ
5
summation by S. C. Milne, a partial fraction decomposition, and analytic continuation. 相似文献
94.
Mahmoud Benkhalifa 《Topology and its Applications》2008,155(12):1350-1370
The purpose of this paper is to classify the quasi-isomorphism classes of 1-connected minimal free cochain algebras over a commutative ring. Our tool to address this problem is a “certain” long sequence, called the Whitehead exact sequence, which we construct for every such algebra. We introduce the notion of coherent isomorphisms between these exact sequences and we show that two 1-connected minimal free cochain algebras are quasi-isomorphic if and only if their respective Whitehead exact sequences are coherently isomorphic. 相似文献
95.
A convergence theorem for the continuous weak approximation of the solution of stochastic differential equations (SDEs) by general one-step methods is proved, which is an extension of a theorem due to Milstein. As an application, uniform second order conditions for a class of continuous stochastic Runge–Kutta methods containing the continuous extension of the second order stochastic Runge–Kutta scheme due to Platen are derived. Further, some coefficients for optimal continuous schemes applicable to Itô SDEs with respect to a multi–dimensional Wiener process are presented. 相似文献
96.
张福财 《大庆师范学院学报》2008,28(6):98-102
从尼克松、福特、卡特到里根、布什时期是美国的“欧洲战略”进行重大调整时期,是冷战行将结束、进入欧盟时期的对欧洲一体化政策“重新审视”的重要历史阶段,美国对欧政策发生了较大变化。 相似文献
97.
The self‐consistent charge density functional tight‐binding theory study of carbon adatoms using tuned Hubbard U parameters
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The self‐consistent charge density functional tight‐binding (DFTB) theory is a useful tool for realizing the electronic structures of large molecular complex systems. In this study, the electronic structure of C61 formed by fullerene C60 with a carbon adatom is analyzed, using the fully localized limit and pseudo self‐interaction correction methods of DFTB to adjust the Hubbard U parameter (DFTB + U). The results show that both the methods used to adjust U can significantly reduce the molecular orbital energy of occupied states localized on the defect carbon atom and improve the gap between highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) of C61. This work will provide a methodological reference point for future DFTB calculations of the electronic structures of carbon materials. 相似文献
98.
Single crystals of the title compound are obtained from a melt of U3O8, MoO3, and excess Cs2CO3 (Pt crucible, 950 °C, 12 h, cooling rate 5 °C/h). 相似文献
99.
Viktor Jobbágy Norbert Kávási János Somlai Borbála Máté Tibor Kovács 《Microchemical Journal》2010,94(2):159-165
Hungary is rich in spring waters. A survey studying the naturally occurring alpha emitter radionuclides in 30 frequently visited and regularly consumed spring waters was conducted out in the Balaton Upland region of Hungary.226Ra, 224Ra, 234U, 238U and 210Po activity concentrations were determined by using alpha spectrometry after separation from matrix elements. Average concentration (mBq L− 1) of 226Ra, 224Ra, 234U, 238U and 210Po in the spring waters is varied from 2.1 to 601, from < 1.1 to 65.4, from 3.9 to 741.9, from < 0.44 to 274.3 and from 2 to 15.2 respectively. In most cases radioactive disequilibrium was observed between uranium and radium isotopes. The doses for the analyzed samples of spring water are in the range 3.59–166.73 μSv y− 1 with an average 18.2 μSv y− 1 .This is well below the 100 μSv y− 1 reference level of the committed effective dose recommended by WHO. Only one water sample had a dose higher than 100 μSv y− 1, mainly due to the contribution from radium (226Ra, 224Ra) and 210Po isotopes. This study provides important information for consumers and authorities about their internal radiological exposure risk from spring water intake. 相似文献
100.
针对目前传统U型渠施工效率低,耗费大的问题,提出了一种自走式U型渠掘进机(以下简称掘进机)的设计方案。介绍了掘进叶片与切土刀片共同作业的U型渠成型方法,对掘进叶片的动力学进行了分析。基于经典切削理论,引入挤碎、输送土壤等因素后,推导出了掘进叶片施工过程的切削合力。确定了影响掘进叶片功率消耗的主要因素。利用滑切原理对切土刀片进行了设计。目前,掘进机已投入使用,承建U型渠道长度达320 km。试验表明掘进机成型的沟渠在顺直性、横断面尺寸标准性、填土密实度达标率等方面均优于传统施工方案。 相似文献